With the advancement of communication technologies, various communication products and technologies have been continuously appearing in the market. Moreover, with integrated circuit (IC) technologies getting matured, the size of product has been gradually developed toward smallness, thinness, shortness and lightness. With respect to an antenna used for radiating or receiving signals in the communication products, the size of the antenna determines if the objective of smallness, thinness, shortness and lightness can be achieved.
An antenna is an element used for radiating or receiving electromagnetic wave, and generally, the features of antenna can be known by the parameters of operation frequency, radiation patterns, reflected loss, and antenna gain, etc. The antennas used in the present wireless communication products must have the advantages of small size, excellent performance and low cost, so as to be popularly accepted and approved by the market. According to different operation requirements, the functions equipped in the communication products are not all the same, and thus there are many varieties of antenna designs used for radiating or receiving signals, such as a rhombic antenna, a turnstile antenna, a microstrip antenna, and an inverted-F antenna, etc., wherein the microstrip antenna has the advantages of small size, light weight, easy fabrication, flexibly forming on a curved surface and being able to form with other electric elements in the same circuit, etc. The conventional microstrip patch antenna's radiating portion (microstrip patch) is about ½ wavelength (λ) long. Therefore, it is an important issue about how to further shrink the size of the microstrip patch antenna.
On the other hand, due to increasing demands of high-speed wireless communication, many new technologies have been continuously adopted in the actual applications, wherein ultra wideband (UWB) is one of the technologies under vigorous development. UWB is a wireless transmission specification using quite a broad bandwidth. The Federal Communications Commission (FCC) regulates that the frequency UWB is ranged in the bandwidth smaller than 1 GHz and the bandwidth between 3.1 GHz and 10.6 GHz, and the bandwidth of UWB can be as large as 500 MHz. However, the bandwidth of the conventional microstrip antenna is too small to meet the requirements of UWB.
Hence, there is an urgent need to develop a microstrip antenna for further reducing the antenna size and providing sufficient bandwidth for overcoming the shortcoming of the conventional technology.